Travel time tomography of the CMB: discrepancy between reflected and refracted phases

We derive 3-D maps of the Earth's mantle, CMB and outer core by means of least squares tomographic inversions. The data set includes compressional wave travel time measurements associated with the phases P, PcP, PKPbc, PKPdf, all based on the bulletins of the International Seismological Centre (1963-1964), after source relocation by Antolik et al., [2002]. Despite the good agreement between the images of the mantle obtained using different core phases, the maps of the CMB derived from core-reflected (PcP) and core-refracted (PKP) phases are not well correlated. We study the radial coherence of whole-Earth tomographic images, to investigate potential trade-offs between CMB undulations and velocity anomalies in the mantle and/or outer core. We find that imaged lateral heterogeneities in the outer core are correlated with the topography of the CMB. This, together with the studies of Wahr and De Vries [1989] and Piersanti et al. [2001], suggests that the core anomalies might not be fictitious; they could be explained physically in terms of gravity-induced perturbations to equipotential surfaces.